This invention concerns a system for enhancing the security of the interface between a consumer electronic device and a removable security device such as the interface defined by the National Renewable Security Standard (NRSS). Security is enhanced by protecting the audio/visual (A/V) stream that is descrambled by the removable security device, such as a smart card, coupled to the consumer electronic device. Examples of consumer electronic devices employing the NRSS smart cards include digital television receivers, digital video cassette recorders as well as separate devices or xe2x80x9cboxesxe2x80x9d that may be located on top of, or coupled to, a television receiver, i.e., set-top boxes.
A concern of today""s emerging digital consumer electronic products is the ability to access a plaintext (i.e., in-the-clear) digital bitstream thereby permitting one to make unauthorized digital copies of the bitstream. The National Renewable Security Standard (NRSS) (EIA-679) developed by the Electronic Industries Alliance provides a means for employing renewable security in connection with digital consumer electronics (CE) devices, for example, digital television receivers, digital video cassette recorders and set-top boxes. Renewable security allows for the development of conditional access systems that can be replaced, upgraded or recovered with minimum cost and effort.
Typically, a service provider will scramble (or encrypt) the signal before it is transmitted or broadcast. A conditional access (CA) device (e.g., an NRSS smart card) may be used to descramble (or decrypt) the signal and route it to the host device. However, a problem with the NRSS architecture is that the audio/visual (A/V) stream is sent to the host device (for example, a display device or a set top box) from the smart card in-the-clear. That is, the A/V stream is not scrambled when it leaves the CA device. Thus a person can monitor this line and use a data capturing device to record all the data.
This invention resides, in part, in recognition of the described problem and, in part, in providing a solution to the problem. Generally, the present invention defines a method for protecting the output audio/visual (A/V) stream of a smart card by receiving a scrambled signal from a source external to said smart card, generating a descrambling key in response to said received signal, descrambling said received signal using said descrambling key to generate a descrambled signal, receiving data from said external source, generating a scrambling key in response to said received data, scrambling said descrambled signal using said scrambling key to generate a rescrambled signal, providing said rescrambled signal to said external source.
In accordance with one aspect of the present the received data is a scrambling key encrypted using a public key associated with said smart card and wherein the step of generating said scrambling key comprises decrypting said encrypted scrambling key using a private key associated with said smart card, said private key being stored in said smart card.
In accordance with one aspect of the present invention, the scrambling key comprises a seed value and the step of scrambling the descrambled signal generating a random sequence in response to the seed value, and generating the rescrambled signal by exclusive ORing said random sequence and said descrambled signal.
In accordance with another aspect of the present invention, the received scrambled signal comprises video, audio and control packets and the seed value is generated, in the external source, in a unique manner in response to said video, audio and control packets.
In accordance with another aspect of the present invention, the smart card verifies the seed value by comparing the seed value to a subsequent seed value generated in the unique manner in response to the video. audio and control packets.
In accordance with yet another aspect of the present invention. the seed value is generated utilizing one of the hash of video, audio and control packets or by exclusive ORing said video, audio and control packets together.
In accordance with yet aspect of the present invention, a first seed value is generated in the smart card and the received data is a second seed value. The step of generating said scrambling key comprises generating said scrambling key in response to said first and second seed values.
In accordance with yet aspect of the present invention, a system for managing access between a service provider and a host device having a smart card coupled is provided. The host device performing the steps of: receiving a scrambled signal from the service provider, sending, to the smart card, a seed value generated in the host device and encrypted using a public key of the smart card, coupling the received signal to the smart card, and receiving from the smart card the rescrambled signal. The smart card has a means for access control processing, comprising means for generating a descrambling key in response to the received signal, means for descrambling the received signal using the descrambling key to generate a descrambled signal, means for decrypting the encrypted seed value using a private key of the smart card to provide the seed value, means for generating a random sequence in response to the seed value and means for scrambling the descrambled signal using the random sequence and the descrambled signal to generate a rescrambled signal.
These and other aspects of the invention will be explained with reference to a preferred embodiment of the invention shown in the accompanying Drawings.